1. Field of the Invention
The present invention relates to a measuring apparatus and a measuring method for measuring a signal-under-test, a testing apparatus and a testing method for testing a device-under-test and an electronic device. More specifically, the invention relates to a measuring apparatus, a measuring method, a testing apparatus and a testing method for measuring jitters in the signal-under-test output from a device-under-test.
2. Related Art
Conventionally, there has been known a test for measuring jitter in a signal-under-test output from an electronic device such as a semiconductor circuit as an item for testing the electronic device. For example, jitter of such signal-under-test is measured by a time interval analyzer, an oscilloscope or the like by inputting the signal-under-test thereto. The time interval analyzer or the like allows such jitter to be calculated by measuring phase errors of edges of the signal-under-test for example.
There is known a function test for judging whether or not a pattern of a signal-under-test output from an electronic device coincides with a pattern of an expected value as an item for testing the electronic device. In this test, a testing apparatus detects a data pattern of the signal-under-test by comparing a voltage value of the signal-under-test outputted out of the electronic device with threshold voltage when a predetermined test pattern is inputted to the electronic device. Then, it judges whether or not the data pattern coincides with the pattern of the expected value.
It has been thus necessary to prepare the apparatus for measuring jitter and the apparatus for testing function in order to carry out the jitter in addition to function tests as described above. Therefore, it has been costly to carry out the jitter test.
Typically, a function testing apparatus compares the voltage value of the signal-under-test with the threshold voltage at preset timing. Therefore, it can detect the edges of the signal-under-test by shifting the comparison timing. It provides timing information when the data pattern of the signal-under-test transits bit by bit. It is then conceivable to measure jitter by utilizing this function, i.e., by using the apparatus for performing functional testing.
However, the conventional apparatus for functional testing is what sets sampling timing in a test rate synchronized with period of the signal-under-test. Therefore, it is necessary to set phase of the sampling timing for each test rate in order to gradually shift the relative phase of the sampling timing with respect to the signal-under-test within each test rate. It has been thus necessary to carry out the cumbersome timing setting in order to carry out the jitter test. Still more, its measuring accuracy has not been suitable for the test because the timing is shifted corresponding to the relative phase.
When jitter is measured by using an oscilloscope or the like, the signal-under-test to be input thereto contains amplitude noise components in addition to the timing noise component. Therefore, it has been difficult to accurately measure only the timing noise of the signal-under-test.
Accordingly, it is an object of the invention to provide a measuring apparatus, a measuring method, a testing apparatus, a testing method and an electronic device, which are capable of solving the above-mentioned problem. This object may be achieved through the combination of features described in independent claims of the invention. Dependent claims thereof specify preferable embodiments of the invention.